Natalie Portman was left in some pain after "dislocated a rib" on the set of her new movie 'Black Swan' because the "super low budget' film couldn't afford to have a medic on stand by.

The 29-year-old plays a ballerina in Darren Aronofsky's film for which she trained for up to eight hours a day.

She told David Letterman: "I injured a rib, I like dislocated a rib, it sort of went under another one, when you get lifted it just sort of went under.

"When I got injured I called the producer, I was like 'Could you get the medic? I need an ice pack or something right now,' and he was like, 'Oh, we don't have a medic because it's super low budget.'

"I have been working for like twenty years, I don't even think that's legal. I was like before you take away a medic, take away my trailer and the next day I didn't have a trailer, I swear to God!"

The already slender star also said that she had to lose weight for the role.

"I think I lost like 20 pounds, I mean I'm 5ft 3in so it was pretty extreme," she said.

"I mean I am back at my healthy weight now, I like eating so I waited until the very end to do the diet part."